The present invention relates to a novel undercoating composition for photolithographic resist layer and a photolithographic patterning resist material by using the undercoating composition. More particularly, the subject matter of the invention is a coating composition for forming an undercoating layer on a substrate surface to be interposed between the substrate surface and a photolithographic resist layer for patterning without the problems of notching or intermixing between the undercoating layer and the photoresist layer thereon and capable of exhibiting a high suppressing effect on the reflection of light from the substrate surface and giving a patterned resist layer having high fidelity to the photomask pattern along with a high selectivity ratio in etching of the undercoating layer as well as a photolithographic resist material for patterning consisting of a substrate and a photoresist layer with intervention of an undercoating layer formed from the undercoating composition.
Along with the trend in recent years in the photolithographic patterning technology for the manufacture of semiconductor devices toward a shorter and shorter wavelength of the light for pattern-wise exposure of a photoresist layer, the patterning work is performed by using the i-line light of 365 nm wavelength, deep ultraviolet light and excimer laser beams as the major current. The pattern-wise exposure of the photoresist by using such a short wavelength light is accompanied by the problem of an increase in the reflection of the light on the substrate surface resulting in the degradation of the quality of the patterned resist layer such as local distortion of the pattern or so-called notching and decrease in the dimensional accuracy of the reproduced pattern. With an object to suppress these disadvantageous phenomena, technological interest is now directed to the so-called ARC (anti-reflective coating) method in which an anti-reflective layer is interposed between the substrate surface and the photoresist layer. Various attempts and proposals have been made heretofore on an undercoating composition for the formation of the anti-reflective undercoating layer for the photoresist layer.
For example, Japanese Patent Kokai 59-93448 discloses a photoresist material in which an anti-reflective undercoating layer containing an ultraviolet absorber is interposed between the substrate surface and the photoresist layer. Since the undercoating composition for the anti-reflective undercoating layer contains a polyamine acid and polybutene sulfonic acid as the resinous ingredient, the adhesion between the anti-reflective coating layer and the substrate surface or photoresist layer is relatively poor resulting in some troubles such as exfoliation of the layers in the lapse of time and formation of scum in the course of the development treatment.
With an object to solve the above described problems, the inventors in Japanese Patent Kokai 6-35201 have proposed an undercoating composition for anti-reflection in photolithography containing a copolymer of glycidyl methacrylate and methyl methacrylate as the resinous ingredient and an ultraviolet absorber. Due to the low compatibility between the ultraviolet absorber and the resinous ingredient, however, the undercoating composition has a limitation in the content of the ultraviolet absorber so that, when the amount of the ultraviolet absorber is in excess of the upper limit, the anti-reflective effect of the undercoating layer cannot be fully exhibited due to intermixing between the undercoating layer and the photoresist layer formed thereon and, in addition, the dimensional fidelity of the patterned resist layer to the photomask pattern cannot be high enough and cannot fully comply with the requirement in the fine and precision patterning in the modern technology for the manufacture of semiconductor devices. While it is desirable in order to accomplish improvements in the working efficiency and fidelity of the patterned photoresist layer to the photomask pattern that the ratio between the etching rate of the undercoating layer and the etching rate of the photoresist layer in the etching treatment to follow patterning of the resist layer or the so-called selectivity ratio should be as high as possible, the above proposed undercoating composition is not quite satisfactory in this regard because the selectivity ratio cannot be high enough with the undercoating composition.